This invention relates to a method for detecting the depth of cracks which occur and develop in the rolls for transferring hot steel ingot blooms either during or out of transferring operation and rolls specifically devised for the method.
Several methods have been heretofore been proposed for the above purpose and such known method substantially comprises:
(i) method utilizing a crack depth meter which operates with a high-frequency current, PA0 (ii) method employing electromagnetic induction, and PA0 (iii) ultra-sonic crack-detecting method.
However, such known methods cannot provide accurate measurement of the cracks, and this is especially true when the rolls which have been used for hot-bloom transferring operation over a considerable time are to be measured. Namely, after such long-time use, many cracks usually occur on the surface of the rolls due to the thermal fatigue making the surface of the roll very coarse. Therefore, the measurement of the depth of the cracks thereafter becomes extremely difficult or impossible.
Accordingly, it is an object of the present invention to provide a method which can readily and accurately detect the depth of cracks in the rolls, thereby providing for accurately judging the expected life of the rolls for repairing or replacing purposes.
It is another object of the present invention to provide rolls which are effectively used for the above method.
In summary, the method for detecting the depth of cracks in the bloom-transferring rolls is carried out in the following manner.
A fluid of desired pressure is fed or supplied into a plurality of elongated holes formed in the rolls. The elongated holes are substantially disposed parallel to and along the axis of each roll and also below and parallel to the round outer surface of the roll. When the cracks occur on the surface of the roll and develop toward the core of the roll, the cracks communicate with the elongated holes, thereby providing a change in the amount of fluid flow. Such change of fluid flow is detected by a suitable detecting means enabling the prompt and accurate detection of the depth of the cracks in the roll. The roll used for the above method can be of any construction so long as the elongated holes are formed therein. For example, the roll may be one which is provided with a cooling water passage on and along the axis of the roll besides the elongated holes.